Children with acquired SAA (ASAA) are at high risk of life-threatening infections without prompt therapy.1 The gold standard treatment is hematopoietic SCT (HSCT) from a matched sibling donor, available in only 25% of cases, with a survival rate of 90%.2 The remaining patients are eligible for immunosuppressive treatment (IST) with a response rate of 60–80%.3 In cases of IST failure and absence of suitable donor, haploidentical HSCT (HHSCT) could be considered. To date, limited reports of the use of purified CD34+ cells are available.2,4,5 In this setting, graft rejection (GR) and opportunistic infection due to delayed immune reconstitution are major causes of transplant failure.4
A 4-year-old African girl was admitted to the Pediatric Hematology Oncology of Padova with fever, bruises, severe pancytopenia and reticulocytopenia. The diagnosis of ASAA was made through BM aspirate (aplasia without myelodysplasia) and trephine biopsy (<10% of cellularity without myelofibrosis).1
As an HLA-identical sibling donor was not available, one course of IST was administered (steroids, rabbit antilymphocyte globulin (rALG), CsA and G-CSF)2 and was complicated by fever and progressive respiratory failure requiring intensive care. Computed tomography (CT) scan showed bilateral multiple areas of parenchymal consolidation and a peribroncheal lesion. Galactomannan antigen (GM) on serum and bronchoalveolar lavage samples became positive (index >0.50). In the presence of ‘probable’ lung aspergillosis, voriconazole was started. The patient worsened in spite of IST there was no improvement in the blood count with concomitant clinical deterioration. Because of the lack of a suitable unrelated donor owing to the rarity of the patient’s HLA, an urgent HHSCT was scheduled. Three months after diagnosis, the patient received HHCST from her mother’s G-CSF-mobilized PBSCs. PBSCs were processed for T-cell receptor alpha beta (TCRαβ) and CD19+ depletion by CliniMACS System (Miltenyi, Cologne, Germany).6 Conditioning regimen consisted of thiothepa (TT; 10 mg/kg), Cy (200 mg/kg) and rATG (Fresenius, Bad Homburg, Germany) (80 mg/kg). No prophylaxis for GVHD was performed. Rapid neutrophil and platelet engraftment was achieved (Table 1) with full donor chimerism. After initial engraftment, the patient developed secondary graft rejection (GR) on day +20, confirmed by chimerism study (100% of the recipient’s cells). Because of worsening of lung aspergillosis in addition to CMV and EBV reactivation, a second HHSCT from her father was done on day +38. Conditioning regimen included TT (10 mg/kg), Cy (200 mg/kg), total lymphoid irradiation (TLI) (7.5 Gy) and rATG (Genzyme, Modena, Italia) (15 mg/kg). Prophylaxis of GVHD consisted of CsA (3 mg/kg i.v.), continued even after PBSC infusion (residual TCRαβ cells in the graft >25 000/kg) (Table 1). Rapid neutrophil and platelet engraftment occurred (Table 1) and full donor chimerism was achieved. No progression of the lung infection was observed in the post-conditioning aplasia period. One month after the second transplant, the peripheral nodules disappeared, the peribroncheal lesion was reduced and GM on serum decreased until negativization. Two and four months after second HHSCT, the patient experienced CMV reactivation with prompt response to preemptive foscarnet. Five months later, despite continuous oral voriconazole, fever recurred. CT scan showed excavation aspects of the known lesion, at risk of endobronchial rupture with GM repositivization in the blood. Surgical lobectomy was successfully performed and the histology confirmed diagnosis of aspergillosis. Thereafter, complete resolution and continuous GM negativity were seen. CsA was stopped 9 months after HSCT. T-, B- and NK-cell reconstitution data are depicted in Figure 1. Neither acute nor chronic GVHD occurred. The regimens were well tolerated without significant toxicity. The patient is currently healthy at 25 months after the second HHSCT, with full donor chimerism and transfusion independency.
HHSCT using αβ-TCR/CD19+ depletion was considered a valid option for our patient in consideration of: (1) IST failure; (2) lack of a suitable donor; and (3) worsening of clinical condition.
This procedure depletes host-reactive donor T cells from hematopoietic stem cell allografts to prevent GVHD, reduces CD19+ cells in order to decrease the risk of EBV-associated lymphoprolipherative syndrome and obtains a product enriched for stem cells and immune cells.6 In particular, high numbers of NK cells in T-cell-depleted PBSC grafts facilitate engraftment and, together with γδ-TCR and monocytes, preserve anti-infective activity.
With regard to the lung aspergillosis, already present before the HHSCT, an improvement was seen with a stable disappearance of GM positivity from the first month after the second HHSCT. The lobectomy was performed to eliminate the risk of endobronchial rupture of the preexistent lesion, which is a well-known complication of aspergillomies. We believe that the infusion of γδ-TCR donor cells controlled the infection during the period of pre-engraftment aplasia, whereas residual immunity of donor cells helped in obtaining a rapid engraftment without GVHD development. Notably, CMV reactivations that occurred until 4 months after HHSCT were well controlled by preemptive therapy without clinical or radiological signs. GR is a cause of transplant failure in the setting of ASAA with an incidence of 10–25%7 and a second transplant is mandatory.8 In our patient, despite initial engraftment, GR occurred early after the first HHSCT. The success of second HHSCT is probably due to (1) higher CD34+ infused cells, (2) different haploidentical donor and (3) second highly immunosuppressive conditioning administered 38 days after the first transplant. In this regard, it is mandatory to enhance recipient immunosuppression in such pathology in which immune system is involved both in the genesis of the disease and GR. As well-known, reduced-intensity conditioning with immunosuppressive drugs used for the treatment of ASAA shows high rate of GR.9 TLI was considered effective and 'safe' in terms of both transplant success and expected toxicity.10
Our findings suggest that HHSCT with αβ-TCR/CD19+ depletion could be a curative treatment option for ASAA patients with no suitable donors, even in the presence of a serious infection. This procedure may offer the following: (1) prompt donor availability for patients with a lower chance of finding a suitable donor; (2) low risk of developing GVHD in the absence of a strong IST; (3) early engraftment with a lower incidence of infections; (4) possibility to transplant even in the presence of critical illness.